I assumed Per Lutken, but looking in the books his initials seemed to be more combined, often together with another No. - then I wondered about Vicke Lindstrand, but that's the wrong country - so I'm back with PL.
The piece seems to be o.k. in most respects - size is 17" x 14.5" (430 x 370mm) and looks the right colour.
So grateful if someone can just confirm this are definitely Lutken's initials please, and thanks for looking.